Pitted fork repair, Sprint Manufacturing 20% uprated springs, and front wheel refit

With the forks removed, I could see how much pitting was present on the stanchions - a lot, as it happens, although each individual pit was pretty small, maybe up to 1mm across.

I decided to try filling them with Chemical Metal epoxy paste on the grounds that, well, it just might work. If not, I'll get them reground and hard chromed. So I degreased them with cellulose thinners and dug as much of the dirt out of the pits as I could with a pin, wiping as i went. Then I mixed up the Chemical Metal a bit at a time and covered the affected areas. It goes off very quickly (about 5 mins) so I had to repeat the process lots of times. 

After leaving it to cure completely overnight, I trimmed back the excess filler with a sharp blade and rubbed the stanchions down with 800 grade wet and dry paper. The finish was smooth and reasonable. I've no idea how robust it will be. 

I'd decided to fit some 20% stiffer replacement fork springs from Sprint Manufacturing. I carefully measured lengths as I went. First, the difference between fully compressed and fully extended is about 145mm. Second, the standard spacer is 110mm. 

The springs I removed were 470mm in length (the shorter, darker spring in the picture below). I would say the 'standard springs', which I believe them to be, but who knows whether a previous owner changed them. The Spring Manufacturing springs were about 490mm in length. I could have cut the spacer down accordingly (to 90mm) but decided I would treat it as an additional 20mm preload to start with and then shorten if required later on. This meant being very careful in compressing the springs to refit the top nut but they went together well.

I decided to try comparing the spring rates. No pics I'm afraid but I did this by placing an old kitchen scales upside down on each of the springs and then compressing them for 1cm. I was surprised to find that the Sprint springs were about 6kg per cm whereas the ones I removed were 6.5kg per cm. In other words, harder. So maybe they aren't the originals. However, the Sprint springs have two pitches  whereas the springs I removed were evenly wound along their entire length. The manual indicates that the originals should be twin rate. I decided I'd try to see what the rate of the Sprint springs are when the close-wound section binds. I did this by clamping the spring in my workmate just above the close-wound section and repeating the scales trick. This time, it showed a rate of 7kg per cm, so about 17% stiffer by my imprecise measurements - close enough to Sprint's claim for me to believe all is in order.

 Forks reassembled, I decided to fit a pair of stone guards. The clamp just above the dust seals. Hopefully, they'll help to keep the Chemical Metal repair functional for a little while at least.

I decided to pull the forks through the yokes slightly more than standard because the stiffer springs would make the bike ride slightly higher than normal, marginally slowing the steering geometry. Again, it's an experiment. The fact that I now know the difference between full extension and compression means I can adjust the down some more as long as I leave at least 145mm between the bottom yoke and fork seals.

I found that the front wheel axel was rusted internally. There is a plastic bung on the left hand end that had been damaged, allowing water ingress. So I cleaned it up with a drill and thin wire brush, primed and painted it before coating the bung in waxoil and refitting. I also gave the front axel nut a birthday.

 I like polishing. The fork top nuts and speedo gearbox gave me a chance to break out the Solvol and bling it up :-)

 Plenty of LM grease on the axel and the wheel is back in place. The axel can be held still with a tommy bar through the left hand end whilst the nut is pinched up. There was zero clearance between the fork legs and the wheel spacer (left) and speedo gearbox (right) so it was a performance getting the wheel in place. I managed it in the end by slackening the fork clamp bolts in the lower yoke and slightly twisting the sliders.

For torquing the axel up, it is necessary to tighten two clamp bolts in the left-hand fork leg so the axel doesn't rotate. The two clamp bolts in the right-hand leg can then be torqued too.

 Handlebars and clocks loose fitted, starting to look like a bike again.